Automatic starter for electric motors



y 1949- B. ANTIPOIVITCH 2,471,135

AUTOMATIC STARTER FO RELECTRIC MOTORS Filed Alig. 24, 1946 5 Sheets-She 1 4 INVENTOR. 5027's AfllZPOUiZCiI y 1949' B. ANTIPOVITCH 2,471,185

AUTOMATIC STARTER FOR ELECTRIC MOTORS Filed Aug. 24, 1946 5 Sheets-Sheet 2 y 4, 1949 B. ANTIPOVITCH 2,471,185

AUTOMATIC STARTER FOR ELECTRIC MOTORS Filed Aug. 24, 1946 5 Sheets-Sheet 3 INVENTOR.

0723 Anlz'povz'ick y 1949- I B. ANTIPOVITCH 2,471,185

AUTOMATIC STARTER FOR ELECTRIC MOTORS Filed Aug. 24, 1946 5 Sheets-Sheet 4 INVENTOR. Boris A72 fz'po vile]:

May 24, 1949.

Filed Aug. 24, 1946 B. ANTIPOVITCH 2,471,185

AUTOMATIC STARTER FOR ELECTRIC MOTORS 5 Sheets-Sheet 5 IN VEN TOR.

Patented May 24, 1949 UNITED STATES PATENT OFFICE AUTOMATIC STARTER FOR ELECTRIC MOTORS Boris Antipovitch, Mexico City, Mexico Application August 24, 1946, Serial No. 692,881

'17 Claims. '1

This invention relatesto a motor controller and-in particular, to anautomatic' apparatus for starting an alternating-current motor on reducedvoltage and then transferring it to full voltage when it has accelerated substantially to full: speed.

'-Various types of starters for alternating-current motors have been known heretofore and it is the object of my invention to improve generally on such devices and particularly to provide a simple, reliable =starter=which can'be manufactured'at relatively-low cost and will function effectively and automatically under a wide variety'ot'condi'tions tostart induction motors or synchronous motors having amortisseur Windings.

Ina preferred embodiment, I provide a magnetic core having a gamer opening therein and an armature adapted tobeattracted by the core when'excited and moved into a position bridging said gap. Anexciting-winding on the core is adapted to be con'nected in series with the-motor to be started and to'apply reduced voltage thereto either by acting as a series reactor or as the secondary portion of an autotransformer or compensator. The armature actuates contacts effective finally to shunt the windings "on the core and'connect the motor directly to its supply lines upon a decrease in the starting current to apred-etermined'value. In one form of the invention and a modification thereof, these shunting contacts are preset by .the attraction of the armatnreto the core and are finally closed by the'release of thearmature on reduction of the starting current as the motor comes up to speed. In another modification, the shunting contacts are those of a contactor, the closing coil of which is energized by release of the armature after first being :attracted. by the core. In still further modifications, the'contactor is operated by the rise in voltage across the supply lines on the motor side of the starter as the starting current fallsofi.

.A. completeunderstanding of the invention may betobtainedifrom the following detailed description and explanation whichreferto the accompanying tdrawings illustrating the several preferred embodimentsand modifications. In the drawings:

Fig.1 is a perspective view of the magnetic core and armature showing diagrammatically the contacts actuated thereby and auxiliarycontrol relays;

j Figs. 2, Band 4 are elevationsshowing the severalsuccessivepositionsof a linkage actuated by 2 the armature effective to close the eontactsconnecting the motor directly to its supplyline, this linkage being omitted from Fig.1;

Fig. 5 is aview similar to Fig. 1 showing a modification in which: the core-has a secondary Winding as well as an exciting winding;

Figs. 6-, 7 and 8 are similar to Figs. 2, 3 and 4 but relate to the modification of Fig. 5;

Fig. 9 is a circuit diagram showing the modification in which the full-voltage orshunting contacts are those of a-scontactor controlled by the armature of the starting-apparatus;

Fig. 10 is a diagram similartoFig. 9 showing a further modification; and

Fig. 11=is a, circuit diagram of a starting device comprising a closed-core reactor and a shunting contactor controlled thereby.

Referring in detailtothe drawings, .and for the present, toFigs. 1 through 5, one form of my invention comprises an E-shaped laminated core I with windings 2a, 2b and :20 on the legs thereof, respectively, adapted to be connected between the windings of a polyphasealternating-current motor and the lines ofa three-phase supply source. An armature 3 ismovable on guide rods 4 into and out ofbridgingengagement with the open side ofthe core, being attracted when the core is excited to apredetermined degree and released when the excitation decreasesbelow the hold-in value. The armature 'is normally maintained in the-illustrated position by compression springs 5 surrounding the rods, the springs yielding under'the attractive force of the core when excited to permit movement of the armature into bridging engagement therewith. The rods 5 are threaded and nuts-6 and! turned thereon limit the upward and downward movements of the armature'and permit adjustment of'the initiaicompressionof the springs. The reactance of the windings :2a, 2b andZc is a miniminn when the armatureis in its upraised position to a maximum :when it is in engagement with the core I.

Relaywindings 8a and 80 connected in series with windingsZa and 2c actuate 'cores 9a and '90 which together control a contact-tripping member IE). This'member is effective by means to be described shortly,"to cause final'engagement of pairs of contacts, Ha and 12a, HI) and i217, and ll c and [20, shunting the reactor windings 2a, 2b and 2c and relay windings to and 80, thereby applying full voltage to themotor when it has come up to speed. A no-voltagerelay M in the form of a C-shaped coreexcited by a winding l3 has an armature 34 which,-when released, causes opening of the contacts Ila, IZa, etc., by means which also take part in the closing thereof, as shown in Figs. 2 through 4, to which reference is now made.

The two groups of contacts Ila, -etc., and I2a, etc., are mounted respectively on blocks I5 and I6 of insulation and the contacts of each group are thus operated simultaneously. A link I! connected to the block I5 and a link I8 form a toggle, the link H and block I5 being pivotal about a stationary pivot pin I9, and the links I! and is being connected by a pivot pin 20. Link l8 has a pivot pin ZI slidable in a slotted guide 22 mounted on any suitable fixed support. A tension spring 23 normally tends to collapse the toggle links ll and I8 when their common pivot pin 253 has been moved past dead center. This is accomplished by a pivotally mounted trigger 25. The trigger is so mounted as to receive a blow from member lfl when the latter is released by the decrease in the energization of windings 8a and 80 to a predetermined value. The toggle links are extended on descent of the armature 3 by a link 25 pivoted on pin 2I and a pin 25a slidable in a slot 39 in a link 26 which is pivoted on the armature. Extension of the toggle links moves contacts Ila, IIb and I I0 from the position shown at A in Fig. 2 to the position shown at C in Fig. 3.

Contacts I2a, I21) and I2c are actuated by toggle links 21 and 28. Link- 28 is pivoted on a fixed pin 29. A pin 30 is the pivot common to the two links. A pin 3i through link 21 is slidable in a slotted guide 32 and connects the link to block I5. A tension spring 33 normally tends to collapse the links when the common pivot pin 30 is actuated past dead center. This is accomplished by a finger extending rearwardly from the pivoted armature 34 normally held up by energization of relay I4. The toggle links 21 and 2e are extended on descent of armature 3 by a link 38 pivoted to pin 30 and pin 25a. The link 38 has a slot 38a in the lower end thereof and a slot 39 is formed in link 26. These slots permit lost motion between links 26 and 38 and between links 25 and 26. When links 21 and 23 are extended, contacts I211, I21), and I2c are moved from position B shown in Fig. 2 to position I) shown in Fig. 3.

A line switch having contacts 36a, 36b and 360 is located between the line and the starting apparatus described above. A disconnect switch having contacts 31a, 31b and 310 is located between the starter and the motor or load. Assuming the disconnect switch to be closed, the motor may be started simply by closing the line switch. The first result of this operation is the excitation of the core I and attraction of the armature 3. A limited current flows through the motor windings, the voltage applied thereto being reduced by the impedance drop through windings 2a, 2b and 2c, the reactance of which is a maximum when the armature is attracted. The relay windings 8a and 8c are energized by this current and raise their armatures and member Ill. Relay I4 also lifts its armature 34 when voltage is applied to the winding I3. This voltage is the same as that applied to the motor windings.

The descent of armature 3, as above explained, moves contacts II a, Illa, etc., from their normal open positions A and B respectively, to positions C and D preparatory to final closing. This closingis delayed, however, until the current through windings 8a and 8c is reduced to a predetermined '4 minimum as the back E. M. F. of motor builds up on acceleration of its rotor. As the motor starting current decreases, armature 3 is lifted from core by springs 5. This reduces the reactance of windings 2a, 2b and 2c and increases the voltage applied to the motor windings causing the rotor to be further accelerated. Because of the lost motion permitted by slots 38a and 39 in links 33 and 26, however, contacts Ila, IZa, etc, are not affected by lifting of the armature. These contacts are closed when the motor current decreases further to such a value that windings 5a and drop their armatures 9a and 90. Member Hi thereupon strikes trigger which turns on its pivot 40 and trips toggle linkage ii, I 8. The resulting collapse of the linkage turns block i 5 back to position A and since block It remains in position D, contacts Ila, I2a, etc., are engaged. This shunts windings 2a, 2b, and 20 as well as windings 8a and 8c and connects the motor directly across the line. On failure of the voltage for any reason, relay it drops its armature 3 5 tripping toggle linkage 2'5, 28 and causing contacts l2a, I22), and I20 to be retracted to position B. This restores the initial conditions and the starting apparatus will again function in the manner explained on restoration of the voltage.

Figs. 5 through 8 show a modified form of starting apparatus generally similar to that described above except that it utilizes auto-transformer action for applying a reduced voltage instead of a series impedance. As shown in the drawings, the core I, in addition to series windings 2a, 2b and 20, has shunt windings 33a, 43b and 30. adapted to be connected in star by engagement of contacts 44 on the armature with fixed contacts 45, when the armature is attracted as a result of the initial excitation of the core. Contacts A4 are mounted on blocks Min of insulation carried by the armature 3. When windings etc, etc. are energized, they cause a low starting voltage to be applied to the motor windings by including in windings 2a, etc., a voltage in opposition to that of the line. A novoltage relay 45 having a winding tea and an armature liib is responsive to the voltage applied to the motor.

Shunting contacts 59a, 50b and 500 carried on insulation blocks Mb on the armature 3 are adapted to engage contacts 52a, 52b and 520 mounted on an insulation block 52d. Block 5211 is controlled by toggle links 54a and 55a similar to links 2'! and 23. This linkage is extended by a link Eta pivoted to armature 3, a bell crank 55%, a link 560, a bell crank 56d and a link Etc. The bell cranks are pivoted on fixed pins 56f and 569. The toggle links 54a and 55a are operated by a spring 57a. The link 55a pivots on a fixed pivot 57b, and the link 54a has a guided slide movement in the slotted guide 570. The initial descent of the armature 3 thus causes contacts tla, etc., to move from position A to Fig. 6 to position C of Fig. 7 and extends the toggle link age 5 1a, 55a thus moving contacts 52a, etc., from position B of Fig. 6 to position D of Fig. '7. While the armature is attracted to the core I, the motor starts under reduced voltage and relay 45 attracts its armature 651). When the starting current is reduced by the back E. M. F. of the motor as it comes up to speed, core I is released. This causes disengagement of contacts Aid and s5 and moves contacts 59a, etc, from position 0 of Fig. '7 to position A of Fig. 8 in which they engage contacts 52a, etc., which remain unmoved by reason of the slot in the link 56a which permits lost motion thereof relative to bell crank 56b.

Eull 1 voltageris; thus applied to the :motor windings. Failure .10]? -iine u=voltage 'for tanywrreason causes. relays to fdlQD'fitS armature bthereby tripping-;:togg1e. linkage 'ii la, v5.5a and restoring initial-conditions.

Figsxi9randp10 .showtwo. further :modifications, each of ,pwhich'gmawbe: applied: toxboth the reactorrand the reactor-.auto-transformer type of starter andiconsistsrof an electromagnetic, switch controlled cbyxthe movement. of -the :armature thereof.

3-Ffig.; 9:illustrates a :magneticswitch-Fi'l controlledyby: an. auxiliary switch. 'On' the. movable armaturei-3i of vcore I anactuating.memberiAB-is mounted. 3A rocker element t"! "is rotatably mounted on-aizfixed pivot .50 and hasaprojection 48*:engagedrby.member on the armature 3 when it is .amoved ;5downwardly. i Spring .49 normally biases" element .41. toward the. position" indicated. On: the same shaftiSl] arm 5 I is mounted and is held against a stop 52 by spring 'A contact 54 is fixed to the end of armSl anda-cooperating contact55 is fixed tothe end of'a flexible leaf spring- 55.

Electromagnetic -.switch 5! includes contacts 2 58a; band- 580 which are connected to the line side of the electromagnet coils wound oncore I, and the'cooperating'contacts sea; 5% and 59c-are connected to the motor side of these-coils. --Solenoid-fifl eflieots closing of thecontacts when; it isenergized. One'end of solenoid {it is connected to the line switch-=contact 6 I b and another" end to the contact-540i the auxiliary switch. Gontact -55 is connected-to the line switch contact Sic. Aux-iliary contact 58d is connected to the .i

line switch contact -6 la and the: otherauxiliary contact 59d-is connected to the other endof coil Bll.

The operation of the circuit. is as follows:

-When line switch contacts 6 log-6 Iband 6Ic "are thecore I. In that movement the member- 46 I again comes in contact with the projection Moi element. 41 rotating it around the shaftill in. an opposite direction. This causes the arm 5| also to rotate around, the shaft and close contacts 54 and"55. 'When the contacts. 54 and ers closed the coilGU is energized. and closes switch 51, thus applying fullline voltage :to the .motor. At. they end. of the movement,. member 46 disengages element 4.1 and the spring .53 opens the contacts 54 and 55.

.As .the auxiliary contacts 58d and .5901 are. closed, the circuit of .the coil is .completedand the switch is held .in position :inspi-te of the fact that contacts .54--.and 55 are opened. *When the current. is switched oiT .theline, coil-6i) releases thecontacts. of switch I], preparing the ci-rcuit for the next-operation.

Anothersystem embodying-an electromagnetic switch is illustrated =in-Fig.; -10. pRieferring to-..jthe latter, electromagnetic switch a: 6T::has-its T0011- tacts 261a, .1611); and 3. B10 ,connectedz-to thesupply lines. .I Ozand :to. one 'end of. the: coils- 62a, Noland 620. -The. other ends of :these coils .-.;are 26011- nected to the motor terminals through switches i I a; .7 Eb; and .I Ic;.and;to;..the :other-..contacts;v of the electromagnetic switchiIiI.

a.Coil;68aoi;switch.61 is connected'.directly across two :oi; the: :motor terminals; .andi hasra: dash-pot i9 connectedto the armature'or stemof switch.

The. operationcofthe system is 'fiSl fOllOWSZ -.When :the line .19 is :energized by closing switches-Illa, :h'lb and Ito the contacts ofiswitoh Glare open. Therefore the currentrflowsthrough the .coilstZagSZb-and 520 to themotor. -Magnetic flux is developed jin-thepcore I .and:.the armature '3 .is attracted. to-the core I againstthe action ofv spring 64. At the same time the voltage is applied tothe coil 68, but is reduced: toia small val-uepbythe-impedance of the :coils F011 armature I and thereafter lowered further to the motor. starting voltageas the armature 3::is :attracted to the core I. The time delay element or. dash-pot fieprevents the possibility of closing of the. contacts. of switchfil' at the-firstzinstant and the coilfis'cannotclose thecontactsof switch 5'! .at the reduced voltage. .As the t current through the coils of core I is-reduced'when the motor gains speed, the springs-.64 lift the armature 3 away from the core I. As the reactance of these coils is decreased and the. current of thexmotor ispreducedi too, the voltage-applied to the -coil-L 68 becomes high enough to :close the'contactsiof switch .61, short-circuiting' the. coils 62.11;. 52b; and BZcand applying full line voltagetmthe motor.

"As 'the'. lines '50 are deenergizedsooil; 68 idrops out to efiect'opening of contacts 61.

A further modification of the automatic starter is shown in'Fig. 11 using a reactorof the closed core type.

a-The circuit comprises a core I on the legs/of which are wound coils 12a;"l'2b and connected to: the corresponding line contacts 13a, 13b; and

730, respectively, on one side and to the corresponding. motor-side contacts' fla, 14b andllc, respectively. The contacts'l'la, 'I'lb and-11c and their corresponding contacts of switch 11 are connected in parallel with the coils 120, 12b and 'izwrespectively. Coil 78 of the magneticswitoh l! is connected to the motor contacts 14b and -Ho.

The operationof the circuit is as follows:

.Whcn line switches 13a, 13b-andl3careclosed to-energize. the line terminals the contacts-of switch *71 are open, hence current flows throughthe reactor coils"'i2a,i"l2b and'TZc. As the motor draws the maximum current, the voltagetoithe 'motor is reduced to the minimum value, hence is unable to operate the magnetic switch 'ia. The motor starts slowly and as it gains speed, thecurrent is'reduced and atthe tiniaihe drop of the voltage across the reactor is decreased, increasing the voltageon the motor andon the-coil of the sWitch'TL When the current through the coils on core I drops to thepredetermined value, increasing to a'correspending degree the voltage across the coi1 'I8 of switch 1?, contacts "I'Iaj'l'lb and l'lc areengaged by their cooperating contacts as switch H closes-and full line voltage is then applied to the motor for normal operation.

.When lineswitchesl3ag'l3b and 730 are opened to 'deenergise the supply lines; switch Tl drops open.

' While'I have illustrated'anddescribed certain specific embodiments .of my invention-it will'tbe and that various changes and modifications may be made within the contemplation of my invention and within the scope of the following claims.

I claim:

1. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, electromagnet means including reactor coils connected in series with said source for limiting the motor starting current including an armature and spring means for biasing said armature away from said coils, and switch contacts operated by said armature for short-circuiting said reactor coils upon a predetermined decrease in motor current flow as the motor increases in speed.

2. An automatic starting system for an alternating current motor comprising, in combination a source of alternating current, electrcmag-- net means including reactor coils connected in series with said source for limiting the motor starting current including an armature and spring means for biasing said armature away from said coils, a toggle operated switch having an operating connection with said armature for short-circuiting said reactor coils upon a predetermined decrease in motor current fiow as the motor increases in speed, and a second electromagnet operable to trip said toggle operated switch and break said short circuit in response to interruption of current flow from said source.

3. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, electromagnet means including reactor coils connected in series with said source for limiting the motor starting current including an armature and spring means for biasing said armature away from said coils, and switch contacts operated by said armature for short-circuiting said reactor coi s upon a predetermined decrease in motor current flow as the motor increases in speed, a plurality of shafts for guiding the movement of said armature towards and away from said coils, a spring encircling each shaft, and a stop means for one end of the corresponding spring and the other stop means for limiting the movement of the armature away from said coils.

4. An automatic starting system for an alternating current motor comprising, in combination, source of alternating current, electromagnet means including reactor coils connected in series with said source for limiting the motor starting current including an armature and spring means for biasing said armature away from said coils, a toggle operated switch having an operating connection with said armature for short-circuiting said reactor coils upon a predetermined decrease in motor current flow as the motor increases in speed, said toggle operated switch including a plurality of pairs of switch contacts, spring operated toggle means connected to one of said pairs of switch contacts and a second spring operated toggle means connected to the other of said pairs of switch contacts, linkage means for connecting both said aforementioned toggle means to said armature, and a second electromagnet for rendering one of said toggle means operative to open said switch upon interruption of current flow from said source.

5. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, a magnetic core having a plurality of legs, a coil around each legand connected in series with one of the lines of said source, switch means for short-circuiting said coils, a second coil wound around each leg, an armature suspended by spring means biasing said armature away from said coil, a second switch means operable by movement of said armature towards said core to insert said second coils in circuit and convert said core and coils to an auto-transformer thereby reducing the voltage applied to the motor in accordance with the ratio of turns of said first and second coils.

6. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, a magnetic core having a plurality of legs, a coil around each leg and connected in series with one oi'the lines of said source, switch means for short-circuiting said coils, a second coil wound around each leg, an armature suspended by spring means biasing said armature away from said coil, a sec-- ond switch means operable by movement of said armature towards said core to insert said second coils in circuit and convert said core and coils to an auto-transformer thereby reducing the voltage applied to the motor in accordance with the ratio of turns of said first and second coils, a plurality of shafts for guiding the movement of said armature towards and away from said coils, a spring encircling each shaft, and a stop means for one end of the corresponding spring and the other stop means for limitin the movement of the armature away from said coils.

7. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, a magnetic core having a plurality of legs, a coil around each leg and connected in series with one of the lines of said source, switch means for short-circuiting said coils, a second coil wound around each leg, an armature suspended by spring means biasing said armature away from said coil, a second switch means operable by movement of said armature towards said core to insert said second coils in circuit and convert said core and coils to an auto-transformer thereby reducing the voltage applied to the motor in accordance with the ratio of turns of said first and second coils, said first mentioned switch means including toggle means connected to said armature and a spring for operatin said toggle means, electromagnetic tripping means responsive to a drop in voltage across said source for causing said spring to operate said toggle means and re-open said first mentioned switch means after closure thereof during the motor starting operation.

8. An automatic starting system for an alternating current motor, comprising a source of alternating current, electromagnet means including reactor coils connected in series with said source for limiting the motor starting current, includin an armature and springs means for urging said armature away from said coils, an auxiliary switch operated by the said armature upon a predetermined decrease in motor current flow as the motor increases speed, an electromagnet means operated by said auxiliary switch including a plurality of pairs of switch contacts, one for each line of the source for short-Circuiting the said reactor coils after the motor has attained its normal current.

9. An automatic starting system for an alternating current motor, comprising a source of alternating current, electromagnet means including reactor coils connected in series with said source for limitin the motor starting current, including an armature and spring means for urging said armature away from said coils, an

electromagnetic switch means for short-circuiting the reactor coils connected to the motor terminal and operated by the increase of the voltage on the motor terminals after the current to the motor is decreased to a predetermined value.

10. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, a magnetic core having a plurality of legs, a coil wound around each leg and connected in series with one of the lines of said source, electromagnetic switch means for short-circuiting the said coils, a second coil wound around each leg, an armature suspended by spring means urging said armature away from said coil, a second switch means operable by movement of said armature towards said core to insert the second coils in circuit and convert said core and coils to an auto-transformer, thereby reducing the volttage applied to the motor in accordance with the M ratio of turns of said first and second coils, an auxiliary switch actuated by the movement of said armature to operate the first mentioned electromagnetic switch means and being connected to the motor terminals and operated by the increase of the voltage while the current to the motor is decreased to the predetermined value.

11. Starting apparatus for an alternatingcurrent motor comprising a magnetic core having a gap therein, an exciting winding on said core adapted to be connected in series with the motor for starting, an armature adapted to bridge said gap when attracted by excitation of the core, means opposing attraction of the armature by the core, switch contacts shunting said winding when engaged, and means rendered operative by movement of said armature away from said core on a predetermined reduction of the current through the motor as it accelerates, causing engagement of said contacts.

12. Starting -apparatus for an alternatingcurrent motor comprising a magnetic core having a gap therein, an exciting winding on said core adapted to be connected in series with the motor for starting, an armature adapted to bridge said gap when attracted by excitation of the core, means opposing attraction of the armature by the core, switch contacts shunting said winding when engaged, means actuated by attraction of the armature to the core for presetting the contacts for engagement, and means actuated on a predetermined reduction in the current through the motor as it accelerates, causing engagement of said contacts.

13. Starting apparatus as defined by claim 12 characterized by said last-mentioned means being actuated by said armature.

14. Starting apparatus as defined by claim 12 characterized by said last-mentioned means being an electro-magnetic trip.

15. An automatic starting system for an alternating current motor comprising, in combination, a source of alternating current, electromagnetic means comprising a core having a group of coils wound therearound, and a movable armature normally biased away from said core, each of said coils being connected in series with a terminal of said source and a motor terminal, a second group of coils wound on said core, a switch operable by attraction of said armature to said core for converting said groups of coils and said core from a voltage limiting reactor into an autotransformer, and means responsive to attainment of a predetermined speed and terminal voltage of said motor for short-circuiting said first group of coils to apply full line voltage to said motor.

16. An automatic starting system for an alternating current electric motor comprising, in combination, a source of alternating current, electro- 5 a second plurality of coils, each wound around one of said legs and having one terminal connected to the corresponding first mentioned coils, a switch operable by said armature for interconnecting the other terminals of said last mentioned coils, which switch, when closed, will convert the coils and core into an autotransformer for reducing the voltage applied to the motor in accordance with the ratio of turns of said first and second mentioned coils and when open, will convert the core and coils into a reactor of variable reactance, depending upon the length of air gap between the armature and legs of said core.

17. A system as recited in claim 16 including a magnetically operated switch having an operating coil connected in parallel with the motor for short-circuiting said first mentioned coils to apply full voltage to the motor after the motor has attained a predetermined speed and after the current has been reduced sufficiently to cause the armature to move away from the core and open said armature actuated switch.

BORIS ANTIPOVITCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,096,922 Korndorfer May 19, 1914 1,511,344 James Oct. 14, 1924 1,840,093 Hardesty Jan. 5, 1932 1,894,928 Wesche Jan. 17, 1933 2,247,655 Fields July 1, 1941 FOREIGN PATENTS Number Country Date 21,357 Great Britain 1909 268,412 Great Britain Apr. 5, 1927 348,097 Italy May 11, 1937 

